Process of tanning hides or skins.



No. 683,294. Patented Dec. l0, l90l.

H'. GARNICHA EL. PROCESS OF TANNING HIDES 0R SKINS.

1 (Application filed Dec. 14, 1896.)

(No Model.)

m5 Norms PETERS co, vnotn unio. wumnm'om o. c;

' UNITED STATES PATENT OFFICE,

HENRY CARMIOHAEL, OF MALDEN, MASSACHUSETTS.

PROCESS OF TANNING HIDES OR SKINS.

SPECIFICATION forming part of Letters Patent N 0. 688,294, dated December 0, 901- Application filed December 14, 1896. Serial No. 615,549. (No specimens.)

To all whom, it may concern:

Be it known that I, HENRY CARMICHAEL, residing in Malden, in the county of MiddleseX and State of Massachusetts, have invented an Improvement in Processes of Tanning Hides or Skins, of which the following, in connection with the accompanying drawings, is a specification, like letters on the drawings representing like parts. 7

My present invention has for its object to provide a simple and eificient process for producing chrome-tanned leather, by which a product more uniform and of higher quality may be obtained withoutloss of skins or hides treated.

In accordancewith this invention the hides or skins after being prepared in the usual manner for tanning are impregnated with a solution ofchromic acid or chromic-acid compounds in a vat containing said solution, and after the hides or skins have become sufficiently impregnated, which may be determined in the manner now commonly practiced by cutting the skin in the thickest part, the

skins are removed from the chromic-acid solution and placed in a second vat, where they are subjected to the action of a solution of a chromic salt, (sometimes termed chromicoxid salt,) preferably chromic chlorid, either neutral or basic, which gradually replaces the chromic acid or chromic compound in the hide or skin and being rendered insoluble in or upon the fiber produces a superior quality of leather. The chromic acid which is displaced slowly diffuses into the surrounding bath liquor. which may be hereinafter referred to as chromic chlorid, is contaminated by the chromic acid diffused from the skin, and this contami nation would present an obstacle for the carrying on of my process of chrome-tanning on a commercial scale owing to the excessively large quantity of chromic chlorid which would be necessary or required to effect the'tanning if provision were not made to neutralize or offset the contamination of the chromic-chlorid solution by the diffused chromic acid, so that the tanning could be effected in a substantially small apparatus and with a substantially small quantity or volume of chromic chlorid. This result is etfected in accordance with this invention by renewing or electronegative metal. I carbon in contact with granulated zinc or with The solution of chromic salt,

practically purifying the contaminated tanning solution, which renewal or purification is preferably accomplished in a separate chamber or vessel connected for convenience with the tanning-vat, so that the contaminated solution may be caused to pass through the purifying or converting chamber or vessel and then back again into the tanning-vat, the said contaminated solution on its passage through the purifying or converting chamber being freed from the contaminating chromic acid and restored to its original or normal chromic condition or state, which renewed chromic solution on its admission into the tanning-vat becomes again active in tanning the hideorskin. ThechromicacidWhic'hcontaminates the chromic solution may be disposed of by the action of any well-known reducing agent, but preferably by exposing it to the action of an oxidizable metal, such as zinc. To insure rapid action, the zinc is employed in a fine state of division and in the presence of more or less acid, such as hydrochloric acid, or it is made strongly electropositive by contact with gascarbon or copper or by means of an outside source of electricity. The zinc is preferably located in the converting or purifying chamber or vessel. I prefer that the zinc or oxidizable metal in the purifyingchamber should be connected with pieces of I prefer to use gasgrids or bars of the latter metal to insure a prompt and energetic action on the contaminated chromio solution. The zinc in the converting or purifying chamber may be kept active or in an energetic condition by means of a free acid, preferably hydrochloric, which is supplied to the said chamber in such small quantities as will permit it to be practically exhausted by combining \viththe zinc before it passes, with the renewed chromic solution, from the purifying-chamber into the tanningvat containing the hides or skins. The chlorid of zinc incidentally produced in the pnrifying vessel and which may be carried over into the tanning-vat does not appear to have any injurious effect upon the hide or skin.

Figure 1 represents in section and elevation a sufficient portion of one form of apparatus with which to practice this invention, and Fig. 2 a modification to be referred to.

Referring to the drawings, A represents a vat, which may be of wood 01' other suitable material and which in practice is designed to contain a solution a of chromic salt, preferably chromium chlorid, the said vessel, as herein shown, having connected to it near its bottom the inlet-pipe a of a pump B, which may be of any desired or suitable construction and which is herein represented as a centrifugal pump. The pump B has its outletpipe a extended over the upper end of a vat,

chamber, or vessel B, provided with a perforated false bottom a upon which is placed a layer of zinc a and preferably a layer a of gas-carbon or a bed composed of a mixture of these bodies. The vessel B at its upper end is provided with a sieve or strainer b of any desired or suitable construction and upon which the liquid from the outlet-pipe a for the pump is discharged: The vessel B constitutes the converter or purifying-chamber of the apparatus herein shown and is provided with a liquid-outlet pipe b' connected to it below the false bottom a and extended up preferably above the level of the layers of zinc and gas-carbon and terminates above the top of the vessel A, so that the liquid passing through the chamber B may flow back into the tanning chamber or vat A. The vat A may and preferably will be provided with an agitator, herein shown as a paddle-wheel B by which the hides or skins placed in the vat A may be kept in motion in the solution a. The converting or purifying chamber B is adapted to be supplied with free acid, preferably hydrochloric, from a supply tank or vessel B provided with a discharge-pipe I), having a cook or valve N, by which the supply of the free acid to the chamber B may be controlled.

In the operation of the apparatus herein shown the hides or skins to be treated after being first impregnated with a solution of chromic acid or its compounds, as now commonly practiced, (and which solution may be composed of about five per cent. of bichromate of potash to the weight of the skins or hides and from two to three percent. of thirtyfive-per-cent. hydrochloric acid,) are removed from the chromic-acid bath or vat (not herein shown) and placed in the chromic-chlorid solution a contained in the vat A, when an examination of the thicker parts of the hides or skins in the chromic-aeid bath shows that the said hides or skins are thoroughly saturated with the chromic-acid solution.

The chromie solution a, may be made by dissolving commercial soluble chrome-green or hydrated oxid of chromium in a minimum amount of hydrochloric acid and making up the bath by an addition of water to a strength of about four-per-cent. solution of chromic chlorid, or the said bath maybe made by passing a solution of bichromate of potash to which hydrochloric acid has been added through the vessel B and diluting the bath to an extent to form about a four-per-cent. solution of chromic chlorid in the vat A. Common salt is preferably added to the solution in the vat A in about the proportion of two parts salt to one part of chromium chlorid to prevent the drawing of the grain and to facilitate diffusion.

The hides or skins saturated with the solution of chromic acid or its compounds are kept in motion in the tanning-vat A by the agitator B or in other suitable manner, and while in the vat A the chromic acid contained in the skins diffuses into and contaminates the chromic-chlorid solution and imparts to the originally green chromic solution in the vat A a yellowish green tint, and the solution a contaminated by the diffused chromic acid from the skins is carried by the pump 13 to the converting or purifying chamber B and discharged from the pipe a upon the sieve b, which serves to prevent the passage of foreign bodiessuch as loose animal fiber, hair, &o.-into contact with the layers of gascarbon and zinc, through which the yellowish-green contaminated tanning solution percolates or passes and becomes freed from the contaminating chromic acid and converted into a purified chromic solution having nearly or quite an emerald-green color, which purified.

or renewed chromic-chlorid solution passes through the pipe 12 back into the tanning-vat A, where it again becomes energetic and acts upon the fiber of the hide and is distributed with great uniformity through the thickness of the skin, replacing the chromic acid, which gradually diifuses out of the hide. This cycle of operations or steps is continued until the hide or skin has been properly tanned, and during the operation the color of the hide or skin passes from yellow to yellowish-green, then to sage-green, and finally to blue. When the thicker parts are colored blue throughout and pieces cut from them resist the action of boiling water without strong contraction, the tanning is completed. For many uses the resistant temperature of 80 centigrade suffices-that is to say, if the pieces cut from the hides or skins resist the action of water heated to 80 eentigrade the said skins will be sulficiently tanned.

In the above process the chromic acid in the skin diffuses slowly out of the skin into the chromic-chlorid bath, the difinsion being resisted by the said bath, which latter seeks to penetrate into the skin to replace the chromic acid.

By the process above described the chromic compound is distributed with great uniformity throughout the thickness of the skins or hides, the grain is very perfectly preserved, and a strong and supple leather produced. The elasticity or extensibility of the leather can to a considerable extent be modified by the extent to which the process is carried and the product adapted to the various uses and methods of finishing leather. The time required to tan the hide or skin depends upon the thickness of the skin or hide, the strength at. t t V in amount to replace the chromic compoundabsorbed by the skin, and so, also, a portion of the contaminated solution in the vat A may be removed from time to time, so as to de-' crease the amount of zinc chlorid and other substances which may collect in the vat A. Furthermore, it is not necessary that the circulation be maintained through the purifier B throughout the period of tanning, for if after running the pump and paddle twelve hours or less the yellow color has disappeared from the skins and from the tanning solution the skins will continue to tan while the machinery is at rest.

I prefer to use the carbon as the electronegative metal; but I do not desire to limit my invention in this respect, as copper may be substituted for the carbon; but this is not deemed so desirable by me, as the chromic chlorid is found to exert a solvent action upon it and the skins are liable to be slightly discolored.

I prefer to use chromic chlorid; but I do .not desire to limit my invention to this particular chromium salt, as other chromium salts, such as chrome-alum and chromic sulfate, may be used, but with lessened effects.

I prefer to effect the purification of the contaminated chromic solution in a chamber or vessel located outside of the tanning-vat; but, if desired, the chamber or vessel B may be suspended in the tanning liquid in the vat A and reliance placed on the difference of density of the liquids to establish circulation.

In order that my invention may be clearly comprehended, I have hereinafter set forth one set of proportions of the ingredients or materials used-namely, one hundred and fifty (150) pounds of .bichromate of potash, one hundred and fifty (150) pounds of common salt, and six hundred (600) gallons of water are placed in the vat A. fier B are placed two hundred(200) pounds of granulated zinc and six hundred (600) pounds of comrninuted retort-carbon and in the vessel 13 seven hundred and fifty (750) pounds ofthirty-five per cent. (35%) of hydrochloric acid. The pump Bis then started and circulation of the liquid in the vat A established through the purifier B and at the same time the valve b is opened to supply the acid to the purifier in a slow stream. When the bath or solution in the vessel A has lost its reddish color and becomes emeraldgreen, the chlorid solution aris in proper condition for the reception of the skins, which to the weight of fourteen hundred (1 ,400) pounds can be floated in the above bath. During the In the puri-' process of tanning additional hydrochloric acid is supplied to the vessel B and permitted to run slowly into the purifier.

In Fig. 1 I have showed a preferred form of apparatus in which the purifying or converting chamber is connected to the tanningvat, so as to return the purified chromicchlorid solution back into the tanning-vat, which is a simple, cheap, and efficient apparatus for carrying on this process; but the essential feature of this process does not depend upon the use of the purifying-chamber, inasmuch as the purifying-chamber, with the electropositive element, may be entirely disconnected from the tanning-vat A-as, for

instance, in Fig. 2, the tanning-vatA is rep-e resented as provided with an outlet-pipe d at its bottom, having a cook or valve (1, by opening which the contaminated tanning solution may. be allowed to run ofi into a'sec- 0nd vat or vessel d which may be designated a waste tank or vessel. The contaminated tanning solution discharged into the waste tank may, for economy, be again purified by passing the same through a separate purifying-chamber; but this is not essential for the tanning of hides or skins in accordance with into the waste-tank.

I claim- 1. The method of tanning hides or skins, which consists in subjectingthe hide or skin impregnated with chromic acid or its compounds, to the action of a solution of achromic salt such as chromicchlorid, and continuing the action of the chromic chlorid upon the hide or skin by maintaining the chromic-salt solution practically free from the contaminating influence of chromic acid difiused from the skin, substantially as described.

2. The method of tanning hides or skins, which consists in immersing the hides or skins impregnated with chromic acid or its compounds,.in a solution of a chromic salt in a vat or vessel, and continuing the action of the chromic salt upon the hide or skin by maintaining that portion of the chromic-salt solution, which acts on the hide or skin, sub stantially free from the contaminating effect of the chromic acid diffused from the skin, substantially as described.

8. The method of tanning hides or skins, which consists in immersing the hides or skins impregnated with chromic acid or its compounds in a solution of chromic salt in a vat or vessel, withdrawing from said vat 0r vessel a portion of the chromic solution contaminated by the chromic acid diifused from the skin or hide, purifying the withdrawn solution from the chromic acid, and returning the purified chromic solution to the said vat or vessel, substantially as and for the purpose specified.

4. The method of tanning hides or skins, which consists in subjecting them to the suc* and second, to the action of a solution of a chromic compound, such as chromic chlorid, while the latter solution is being, part by part, exposed to the action of metallic zinc made electropositive in the presence of an acid, substantially as described.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

HENRY OARMICIIAEL,

Witnesses:

J AS. H. CHURCHILL, J. MURPHY. 

